Methods and apparatus for thermal compensation during additive manufacturing

ABSTRACT

A method for thermal compensation during an additive manufacturing process. In some aspects, the method may include receiving, at a CNC machine, information relating to a material used in the additive manufacturing process, wherein the received information includes at least a Coefficient for Thermal Expansion (CTE) for the material. The method may further include modifying a distance of travel for a first pre-programmed tool path based on at least the Coefficient for Thermal Expansion (CTE).

TECHNICAL FIELD

Aspects of the present disclosure relate to apparatus and methods forfabricating components. In some instances, aspects of the presentdisclosure relate to apparatus and methods for fabricating components(such as, e.g., automobile parts, medical devices, machine components,consumer products, etc.) via additive manufacturing techniques orprocesses, such as, e.g., three-dimensional (3D) printing.

BACKGROUND

Additive manufacturing techniques and processes generally involve thebuildup of one or more materials, e.g., layering, to make a net or nearnet shape (NNS) object, in contrast to subtractive manufacturingmethods. Though “additive manufacturing” is an industry standard term(ASTM F2792), additive manufacturing encompasses various manufacturingand prototyping techniques known under a variety of names, including,e.g., freeform fabrication, 3D printing, rapid prototyping/tooling, etc.Additive manufacturing techniques may be used to fabricate simple orcomplex components from a wide variety of materials. For example, afreestanding object may be fabricated from a computer-aided design (CAD)model.

A particular type of additive manufacturing is commonly known as 3Dprinting. One such process, commonly referred to as Fused DepositionModeling (FDM), or Fused Layer Modeling (FLM), comprises melting a thinlayer of thermoplastic material and applying this material in layers toproduce a final part. This is commonly accomplished by passing acontinuous, thin filament of thermoplastic material through a heatednozzle, or by passing thermoplastic material into an extruder, with anattached nozzle, which melts the thermoplastic material and applies itto the structure being printed, building up the structure. The heatedmaterial may be applied to the existing structure in layers, melting andfusing with the existing material to produce a solid finished part.

The filament used in the aforementioned process may be produced, forexample, by using a plastic extruder. This plastic extruder include asteel screw configured to rotate inside of a heated steel barrel.Thermoplastic material in the form of small pellets may be introducedinto one end of the rotating screw. Friction from the rotating screw,combined with heat from the barrel, may soften the plastic, which maythen be forced under pressure through a small round opening in a diethat is attached to the front of the extruder barrel. In doing so, a“string” of material may be extruded, after which the extruded “string”of material may be cooled and coiled up for use in a 3D printer or otheradditive manufacturing system.

Melting a thin filament of material in order to 3D print an item may bea slow process, which may be suitable for producing relatively smallitems or a limited number of items. The melted filament approach to 3Dprinting may be too slow to manufacture large items. However, thefundamental process of 3D printing using molten thermoplastic materialsmay offer advantages for the manufacture of larger parts or a largernumber of items.

A common method of additive manufacturing, or 3D printing, may includeforming and extruding a bead of flowable material (e.g., moltenthermoplastic), applying the bead of material in a strata of layers toform a facsimile of an article, and machining the facsimile to producean end product. Such a process may be achieved using an extruder mountedon a computer numeric controlled (CNC) machine with controlled motionalong at least the x-, y-, and z-axes. In some cases, the flowablematerial, such as, e.g., molten thermoplastic material, may be infusedwith a reinforcing material (e.g., strands of fiber or combination ofmaterials) to enhance the material's strength.

In some instances, the process of 3D printing a part may involve atwo-step process. For example, the process may utilize a large printbead to achieve an accurate final size and shape. This two-step process,commonly referred to as near-net-shape, may begin by printing a part toa size slightly larger than needed, then machining, milling, or routingthe part to the final size and shape. The additional time required totrim the part to a final size may be compensated for by the fasterprinting process.

Thermoplastic materials used in additive manufacturing processes maygenerally expand when heated and contract or otherwise shrink whencooled. The amount the material expands and contracts per unit ofdistance per unit of temperature is generally referred to as theCoefficient of Thermal Expansion (CTE). When a material is heated aboveits melting point, the material typically will soften and subsequentlyre-harden or cure when again cooled. This transition from a meltedmaterial to a solid generally occurs at a relatively high temperature.The additive manufacturing processes discussed herein generally occur ator near this melting point. Once a printed part begins to cool andharden, the part may shrink or otherwise contract as the part'stemperature continues to drop until the part reaches the ambienttemperature of the surrounding environment. Since in the near net shapeprocess, the printed part will generally be machined at ambienttemperature and since the cooling and shrinking process may cause asignificant reduction in the size of the printed structure, especiallyfor large parts, in many cases it is necessary to print the part to arelatively larger size to ensure that the part size after coolingmaintains a sufficiently large dimension to maintain trim stock tosupport the machining or trimming process required to achieve the finalnet size.

Fiber filler such as glass or carbon fiber may be commonly used inthermoplastic materials for applications such as industrial tooling.Fiber reinforcement in thermoplastic materials may introduce additionalcomplexity. During the extrusion and printing process, fibers within thesoftened material tend to align with the direction of the print bead.This fiber alignment tends to reduce the expansion and contraction alongthe direction of the print bead as compared to expansion and contractionin directions perpendicular to the print bead. Thus the printed part,which may include print beads oriented in a multitude of directions,will normally expand and contract as a reaction to temperature changesat different rates in different directions.

Such asymmetric expansion and contraction may affect both the initialprinting process, as the part transitions from a generally liquid stateto a generally solid state at room temperature, as well as when a roomtemperature part is machined to its final net size and shape, which maybe heated for use at an elevated temperature.

Industrial tooling normally needs to function at a pre-determined sizeand shape and in many cases this size and shape must be correct at anelevated working temperature. Therefore, a method must be employed toadjust the printing and trimming processes to allow for the normalexpansion and contraction that occurs with thermoplastic materials andspecifically with the asymmetric expansion and contraction that occurswith a fiber reinforced thermoplastic material(s).

In the practice of the aforementioned process, a major deficiency hasbeen noted. The one way of addressing these requirements is to modifythe CNC print and CNC trim programs to allow for shrink in the printprocess and expansion in the trim process, creating new modifiedprograms which are then processed. This can be a difficult and timeconsuming programming process particularly when dealing with fiberreinforced thermoplastics, which may require that, among other thingsthe part be modified at different rates in different directions.Especially since 3D printing software today does not generally supportthese functions. Also, the ambient temperature is a parameter that mustbe used in developing the modified programs and if the actualtemperature when the process is conducted differs from that used indeveloping the modified programs, errors can occur. Another difficultymay be with dealing with a multitude of CNC programs for the same partthat differ only by small amounts. Such variations can be confusing tooperators and lead to errors.

SUMMARY

Aspects of the present disclosure relate to, among other things, methodsand apparatus for fabricating components via additive manufacturing or3D printing techniques. Each of the aspects disclosed herein may includeone or more of the features described in connection with any of theother disclosed aspects. In one aspect, the present disclosure relatesto a method of compensating for thermal expansion and contraction inthermoplastic composite structures at the CNC control instead ofmodifying the CNC program.

In one embodiment of a printing process performed on a CNC machine, anoperator selects the specific material used in a printing operation froma list of materials that have been pre-programmed with certainparameters including the CTE along each of three mutually perpendicularaxes. The operator also may program the CNC machine to compensate forany part shrinkage that may occur upon cooling of the thermoplasticmaterial. The CNC machine may then proceed to print the desired part ata size that is larger than specified by the CNC program by an amountthat compensates for the amount the printed part will shrink in each ofthe three mutually perpendicular axes.

In a subsequent trim process, the part must be trimmed to a size that issmaller than required so that when the part is heated to its workingtemperature, the part will expand to the correct size. In this case, byspecifying the current ambient temperature, which is the temperature atwhich the part will be machined, and the temperature at which the partwill be used, the CNC controller can use the CTE values for the partalong each axis to determine the amount the part will expand in each ofthe three directions. The control system may then trim the part at asize that is smaller than specified by the CNC program, which definesthe final working size and shape, by an amount that compensates for theamount the printed part will expand in each of the three mutuallyperpendicular axes when the part is heated during use.

Additional flexibility can be introduced into the printing or trimmingprocess by allowing the machine operator to manually input CTE valuesfor each axis for desired thermoplastic materials. The manually inputCTE values can then be used instead of the stored numbers associatedwith the material being processed. There are multiple methods by whichthe control can perform these functions. The most direct is to determinean amount to add or subtract per unit of distance along each axis ofmovement to account for shrink or expansion and then add or subtractthat amount per unit of distance traveled by each axis as it executesthe commands in the CNC program.

An alternate method of adjusting motion to account for shrink orexpansion is to modify a feature, which is common on CNC controls,called “scaling factor.” The scaling factor defines the relationshipbetween rotation of the servomotor and linear axis motion. When a CNCprogram is executed, the program is configured to instruct theservomotor to rotate an amount necessary to achieve the axis motionspecified in the CNC program motion command. The CNC control adjusts themachine motion to compensate for thermal expansion or shrink bymodifying the scaling factor so that the axis moves either more or lessin response to the rotation command. In this way, as the controlexecutes the net shape CNC program, the resulting machine motion createsa part that is larger or smaller as defined by the modified scalingfactor.

As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchas a process, method, article, or apparatus. The term “exemplary” isused in the sense of “example,” rather than “ideal.”

It may be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the disclosure, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary aspects of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a perspective view of an exemplary CNC machine operablepursuant to an additive manufacturing process to form articles,according to an aspect of the present disclosure;

FIG. 2 is an enlarged perspective view of an exemplary carrier andapplicator head assembly, including an exemplary roller, of theexemplary CNC machine shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view of an exemplary applicatorhead assembly, including an exemplary roller, shown in FIG. 2 duringuse;

FIG. 4 depicts a flowchart of an exemplary method for adding orsubtracting the expansion or shrink of a desired thermoplastic materialto a CNC program to create a part of a desired size; and

FIG. 5 depicts a flowchart of an exemplary method for modifying thescaling factor for a CNC program to take account for expansion or shrinkduring the creation of a part of a desired size.

DETAILED DESCRIPTION

The present disclosure is drawn to, among other things, methods andapparatus for fabricating components via additive manufacturing, suchas, e.g., via 3D printing. Specifically, the methods and apparatusdescribed herein may be drawn to methods and apparatus for compensatingdimensional changes during to thermal expansions and/or contractions inthe material used in a 3D manufacturing process. As alluded to above,thermoplastic materials may expand when heated and contract or otherwiseshrink when cooled. Thus, consideration must be given to performing amanufacturing process at temperatures different than the temperature(s)prior or subsequent manufacturing processes are performed. Aspects ofthe present disclosure contemplates compensating for thermal expansionand contraction in 3D printing/manufacturing processes in a number ofmanners. For example, in one aspect, the present disclosure contemplatesprinting a part or component to a dimension larger than desired, inanticipating of contraction or shrink that may occur in one or moredirections when the material of the part or component cools. In anotheraspect, the present disclosure contemplates machining or otherwisetrimming the part to a dimension smaller than desired, in anticipationof expansion that may occur in one or more directions when the materialof the part is heated to a working temperature higher than thetemperature at which the part was machined or trimmed.

For purposes of brevity, the methods and apparatus described herein willbe discussed in connection with the fabrication of parts fromthermoplastic materials. However, those of ordinary skill in the artwill readily recognize that the disclosed apparatus and methods may beused with any flowable material suitable for additive manufacturing.

Referring to FIG. 1, there is illustrated a CNC machine 1 embodyingaspects of the present disclosure. A controller (not shown) may beoperatively connected to CNC machine 1 for displacing an applicationnozzle along a longitudinal line of travel, or x-axis, a transverse lineof travel, or a y-axis, and a vertical line of travel, or z-axis, inaccordance with a program inputted or loaded into the controller forperforming an additive manufacturing process to form a desiredcomponent. CNC machine 1 may be configured to print or otherwise build3D parts from digital representations of the 3D parts (e.g., AMF and STLformat files) programmed into the controller.

For example, in an extrusion-based additive manufacturing system, a 3Dpart may be printed from a digital representation of the 3D part in alayer-by-layer manner by extruding a flowable material (e.g.,thermoplastic material with or without reinforcements). The flowablematerial may be extruded through an extrusion tip or nozzle carried by aprint head of the system, and the flowable material may be deposited asa sequence of beads or layers on a substrate in an x-y plane. Theextruded, flowable material may fuse to a previously deposited layer ofmaterial and may solidify upon a drop in temperature. The position ofthe print head relative to the substrate may then be incrementallyadvanced along a z-axis (perpendicular to the x-y plane), and theprocess may then be repeated to form a 3D part resembling the digitalrepresentation.

Machine 1 shown in FIG. 1 includes a bed 20 provided with a pair oftransversely spaced side walls 21 and 22, a printing gantry 23 and atrimming gantry 36 supported on opposing side walls 21 and 22, acarriage 24 mounted on printing gantry 23, a carrier 25 mounted oncarriage 24, an extruder 61, and an applicator assembly 43 mounted oncarrier 25. Located on bed 20 between side walls 21 and 22 is aworktable 27 provided with a support surface. The support surface may bedisposed in an x-y plane and may be fixed or displaceable along anx-axis and/or a y-axis. For example, in a displaceable version,worktable 27 may be displaceable along a set of rails mounted on bed 20.Displacement of worktable 27 may be achieved using one or moreservomotors and one or more of rails 28 and 29 mounted on bed 20 andoperatively connected to worktable 27. Printing gantry 23 is disposedalong a y-axis, supported on side walls 21 and 22. In FIG. 1, printinggantry 23 is mounted on a set of guide rails 28, 29, which are locatedalong a top surface of side walls 21 and 22.

Printing gantry 23 may either be fixedly or displaceably mounted, and,in some aspects, printing gantry 23 may be disposed along an x-axis. Inan exemplary displaceable version, one or more servomotors may controlmovement of printing gantry 23. For example, one or more servomotors maybe mounted on printing gantry 23 and operatively connected to tracks,e.g., guide rails 28, 29, provided on the side walls 21 and 22 of bed20.

Carriage 24 is supported on printing gantry 23 and is provided with asupport member 30 mounted on and displaceable along one or more guiderails 31, 32, and 33 provided on printing gantry 23. Carriage 24 may bedisplaceable along a y-axis on one or more guide rails 31, 32, and 33 bya servomotor mounted on printing gantry 23 and operatively connected tosupport member 30. Carrier 25 is mounted on one or more verticallydisposed guide rails 34 and 35 supported on carriage 24 for displacementof carrier 25 relative to carriage 24 along a z-axis. Carrier 25 may bedisplaceable along the z-axis by a servomotor mounted on carriage 24 andoperatively connected to carrier 25.

As best shown in FIG. 2, mounted to the bottom of carrier 25 is apositive displacement gear pump 62, which may be driven by a servomotor63, through a gearbox 64. Gear pump 62 may receive molten plastic froman extruder 61, shown in FIG. 1. A compression roller 59 for compressingdeposited flowable material (e.g., thermoplastic material) may bemounted on a carrier bracket 47. Roller 59 may be movably mounted oncarrier bracket 47, for example, rotatably or pivotably mounted. Roller59 may be mounted so that a center portion of roller 59 is aligned witha nozzle 51, and roller 59 may be oriented tangentially to nozzle 51.Roller 59 may be mounted relative to nozzle 51 so that material, e.g.,one or more beads of flowable material (such as thermoplastic resins),discharged from nozzle 51 is smoothed, flattened, leveled, and/orcompressed by roller 59, as depicted in FIG. 3. One or more servomotors60 may be configured to move, e.g., rotationally displace, carrierbracket 47 via a pulley 56 and belt 65 arrangement. In some embodiments,carrier bracket 47 may be rotationally displaced via a sprocket anddrive-chain arrangement (not shown), or by any other suitable mechanism.

With continuing with reference to FIG. 3, applicator head 43 may includea housing 46 with a roller bearing 49 mounted therein. Carrier bracket47 may be mounted, e.g., fixedly mounted, to an adaptor sleeve 50,journaled in roller bearing 49. Roller bearing 49 may allow roller 59 torotate about nozzle 51. As nozzle 51 extrudes material 53, rollerbearing 49 may rotate, allowing roller 59 to rotate relative to nozzle51 in order to follow behind the path of nozzle 51 to flatten depositedmaterial 53 as nozzle 51 moves in different directions. As shown in FIG.3, an oversized molten bead of a flowable material 53 (e.g., athermoplastic material) under pressure from a source disposed on carrier25 (e.g., one or more extruder 61 and an associated polymer or gearpump) may be flowed to applicator head 43, which may be fixedly (orremovably) connected to, and in communication with, nozzle 51. In use,flowable material 53 (e.g., melted thermoplastic material) may be heatedsufficiently to form a large molten bead thereof, which may be deliveredthrough applicator nozzle 51 to form multiple rows of deposited material53 on a surface of worktable 27. In some embodiments, beads of moltenmaterial deposited by nozzle 51 may be substantially round in shapeprior to being compressed by roller 59. Exemplary large beads may rangein size from approximately 0.4 inches to over 1 inch in diameter. Forexample, a 0.5 inch bead may be deposited by nozzle 51 and thenflattened by roller 59 to a layer approximately 0.2 inches thick byapproximately 0.83 inches wide. Such large beads of molten material maybe flattened, leveled, smoothed, and/or fused to adjoining layers byroller 59. Each successive printed layer may not cool below thetemperature at which proper layer-to-layer bonding occurs before thenext layer is added.

In some embodiments, flowable material 53 may include a suitablereinforcing material, such as, e.g., fibers, that may facilitate andenhance the fusion of adjacent layers of extruded flowable material 53.In some aspects, flowable material 53 may be heated sufficiently to forma molten bead and may be delivered through nozzle 51 to form multiplerows of deposited flowable material onto a surface of worktable 27. Insome aspects, flowable material 53 delivered onto a surface of worktable27 may be free of trapped air, the rows of deposited material may beuniform, and/or the deposited material may be smooth. For example,flowable material 53 may be flattened, leveled, and/or fused toadjoining layers by any suitable means (e.g., roller 59), to form anarticle. In some embodiments, a tangentially oriented roller 59 may beused to compress flowable material 53 discharged from nozzle 51.

Although roller 59 is depicted as being integral with applicator head43, roller 59 may be separate and discrete from applicator head 43. Insome embodiments, roller 59 may be removably mounted to machine 1. Forexample, different sized or shaped rollers 59 may be interchangeablymounted on machine 1, depending, e.g., on the type of flowable material53 and/or desired characteristics of the rows of deposited flowablematerial formed on worktable 27.

In some embodiments, machine 1 may include a velocimetry assembly (ormultiple velocimetry assemblies) configured to determine flow rates(e.g., velocities and/or volumetric flow rates) of deposited flowablematerial 53 being delivered from applicator head 43. The velocimetryassembly may transmit signals relating to the determined flow rates tothe aforementioned controller coupled to machine 1, which then mayutilize the received information to compensate for variations in thematerial flow rates.

In the course of fabricating an article or component, pursuant to themethods described herein, the control system of machine 1, in executingthe inputted program, may control several servomotors described above todisplace gantry 23 along the x-axis, displace carriage 24 along they-axis, displace carrier 25 along the z-axis, and/or rotate carrierbracket 47 about the z-axis while nozzle 51 deposits flowable material53 and roller 59 compresses the deposited material. In some embodiments,roller 59 may compress flowable material 53 in uniform, smooth rows.

Housing 46 may include one or more barb fittings 67, 68. Coolant mayenter a barb fitting 67 and may be introduced inside of housing 46. Aninlet portion of barb fitting 67 may be fluidly connected to a source ofcoolant (not shown). Once within housing 46, the coolant may absorb heatand may cool housing 46 as it flows within housing 46. Housing 46 mayinclude one or more coolant paths (not shown), which may be disposedwithin housing 46 to direct the coolant within housing 46 duringoperation of machine 1, e.g., when printing a part. The coolant may exitfrom one or more barb fittings 68 and may return to a chiller to becooled back down to an appropriate temperature. The coolant may becooled down to a temperature below that at which deposited material 53may begin to adhere to roller 59. This temperature may vary depending onthe type of material 53 used and may be below the melting point of thatmaterial. In some examples, the coolant may be a liquid coolant, suchas, e.g., water, antifreeze, ethylene glycol, diethylene glycol,propylene glycol, betaine, or any other suitable liquid coolants orcombinations thereof.

Air may enter a quick disconnect 69, which may connect an interiorregion of housing 46 to an air source and/or to ambient air surroundinghousing 46. The air entering quick disconnect 69 may cool down housing46 as it flows within housing 46. In some embodiments, housing 46 mayinclude one or more flow paths (not shown) to direct the flow of airwithin housing 46. The air may exit housing 46 from an outlet openingdisposed on a bottom region of housing 46 onto roller 59 and/or throughpassageways in roller 59. In this manner, air exiting from the outletopening may be used to cool roller 59. For example, air may be directedonto the outside of roller 59 to cool roller 59. Air may travel along aportion of an outer surface of roller 59 or along the entire outersurface of roller 59, cooling roller 59. In some embodiments, roller 59may include one or more hollow, inner portions, and air may be directedwithin the hollow inner portion(s) to cool roller 59 from an innersurface. In some embodiments, air may be directed both onto the outersurface and along a hollow inner region of roller 59.

As alluded to above, the contemplated manufacturing processes may needto accommodate for size variations resulting from thermalcharacteristics of the thermoplastic material used in, e.g., a 3Dprinting manufacturing process. For example, a particular thermoplasticmaterial may expand when heated and contract when cooled.

As a result, any part or component fabricated from the thermoplasticmaterial may also expand and contract when heated and cooled,respectively. As those of ordinary skill in the art will understand, theamount of expansion and contraction a thermoplastic material may undergois dependent the material's property, including, but not limited to, thematerial's Coefficient of Thermal Expansion (CTE). As those of ordinaryskill in the art will also understand, a particular material may expandor contract by different amounts in various direction.

As a result of such expansion and contraction, aspects of thecontemplated manufacturing processes may need to be modified tocompensate for any expansion or contraction caused by thermal changes.In one example, a 3D printed part may be fabricated with one or moredimensions larger than the required dimension. In this manner, themanufacturing process may accommodate any shrinkage of the part as aresult of cooling of the printed part. The description below provides anexemplary method for calculating the required increase in the part'sdimensions to accommodate such thermal contraction. In another example,the manufacturing process may accommodate any expansion of a part thatresults from using the part in an environment having an elevatedtemperature relative to the temperature of the manufacturing process. Inthis manner, the part may be fabricated (e.g., trimmed) to one or moredimensions smaller than the required dimension. The description belowprovides an exemplary method for calculating the required decrease inthe part's dimension to accommodate such thermal expansion.

As alluded to above, there are multiple methods for accommodatingchanges in size caused by thermal expansion and/or contraction. In oneaspect of the present disclosure, a CNC controller, based on the CTE ofa thermoplastic material being used in a manufacturing process maydetermine an amount to add or subtract per unit of distance along eachaxis of movement of the CNC print head to account for shrink orexpansion, and then add or subtract that amount per unit of distancetraveled by the CNC print head in each axis as the CNC controllerexecutes the commands in the CNC program.

With reference now to FIG. 4, in the printing or trimming process, anoperator may select the material being printed or trimmed (step 70) froma list of materials that have been pre-programmed with certainparameters, including, but not limited to, the material's CTE along eachof three mutually perpendicular axes. The operator may then instruct theCNC controller to compensate for any shrinkage or expansion that mayoccur when the finally printed part is cooled or otherwise returned toroom temperature. The parameters defining the CTE of the part in eachdirection are specified in the material definition as is the temperatureat which this particular material prints, the ambient temperature atwhich the material is be printed or trimmed, and the working temperatureat which the material will be used. Then, the CNC program executes themovements necessary to print (or trim) the part at the final size, step71. In doing so, the CNC controller examines the first line of code todetermine the axes used and distance to travel, step 72. The CNC controlcan then adjust the print or trim pattern based on the material shrinkor expansion properties and the temperature difference between theprinting temperature, ambient temperature, and/or working temperature ofthe part, step 73. The CNC controller may then execute the specific lineof code modified to move the print or trim head the new calculateddistance, step 74. The CNC controller may then examine the next line ofcode in the CNC program to again determine the axes used and/or distanceto travel, step 75. Looking at this next line of code in the CNCprogram, the controller decides at step 76 whether to continue at step73 or to end the program. Finally, when the program is complete thecontrol ends the process, step 77. The control system prints or trimsthe part at a size that is larger or smaller than specified by the CNCprogram by an amount that compensates for the amount the printed ortrimmed part will shrink or expand in each of the three mutuallyperpendicular axes. Additional flexibility can be introduced into theprinting or trimming process by allowing the machine operator tomanually input CTE numbers for each axis which can then be used insteadof the stored numbers associated with the material being processed.Similarly, additional flexibility can be introduced by allowing theoperator to manually adjust the distance of travel for each axis.

Turning now to FIG. 5, an alternate method of adjusting motion toaccount for shrink or expansion may include, but is not limited to,using a feature common on CNC controls but typically used in anunrelated manner. Motion along an axis on CNC machines is generallyachieved using a servomotor with some form of rotational feedback thatinforms the CNC controller of the rotational position of the servomotordrive shaft. This drive shaft is mechanically connected to some form ofmechanism (e.g., a gear mechanism having a plurality of rations) thattranslates rotation of the servomotor into linear travel along an axisof motion. In this arrangement, a certain amount of rotation of theservomotor translates to a specific amount of linear motion. To functionproperly, the CNC controller must know this ratio of rotary motion ofthe drive motor to linear motion. To accomplish this, CNC controllerscommonly employ a “scaling factor” which can be programmed to define therelationship between rotation of the servomotor and linear axis motion.In some embodiments, the gearing ration between the rotation of theservomotor and the linear axis motion may be adjusted. When a CNCprogram is executed, the CNC program may instruct the servomotor torotate an amount necessary to achieve the linear axis motion specifiedin the CNC program motion command. The second method of adjustingmachine motion to compensate for thermal expansion or shrink includesmodifying the scaling factor so that the axis moves either more or lessin response to the same rotation command from the control to theservomotor. In this way, as the control executes the net shape CNCprogram, the resulting machine motion creates a part that is larger orsmaller as defined by the modified scaling factor.

As shown in FIG. 5, the operator may select the material being printedor trimmed (step 80) from a list of materials that have beenpre-programmed with certain parameters, including, but not limited tothe CTE along each of three mutually perpendicular axes. Subsequently,the operator may instruct the CNC controller to compensate for theshrink or expansion that may occur in the final part. The CNC controllermay then modify the “scaling factor” to move either more or less foreach axis based on the parameters, including CTE, which was selectedwhen the material was selected, step 81. Then, the operator pushes thecycle start button to start the CNC program, step 82. The CNC controllermay then examines the first line of code to determine the axes used anddistance to travel, step 83. The CNC controller then executes that lineof code moving the print or trim head the altered distance based on themodified scaling factor, step 84. The CNC controller subsequentlyexamines the next line of code to again determine the axes used anddistance to travel, step 85. Looking at the next line of code, the CNCcontroller decides in step 86 whether to continue at step 83 or to endthe program. Finally, when the program is complete the control ends theprocess, step 87.

From the foregoing detailed description, it will be evident that thereare a number of changes, adaptations and modifications of the presentinvention which come within the province of those persons havingordinary skill in the art to which the aforementioned inventionpertains. However, it is intended that all such variations not departingfrom the spirit of the invention be considered as within the scopethereof as limited by the appended claims.

What is claimed is:
 1. A method for thermal compensation during anadditive manufacturing process, the method comprising: receiving, at aCNC machine, information relating to a material used in the additivemanufacturing process, wherein the received information includes atleast a Coefficient for Thermal Expansion (CTE) for the material; andmodifying a distance of travel for a first pre-programmed tool pathbased on at least the Coefficient for Thermal Expansion (CTE); whereinthe CNC machine includes at least one servomotor for linearlytranslating a nozzle along the first pre-programmed tool path; whereinrotational motion of the servomotor is configured to linearly translatethe nozzle via a gearing mechanism; and wherein modifying the distanceof travel for the first pre-programmed tool path includes adjusting thegearing mechanism.
 2. The method of claim 1, wherein the material is athermoplastic material that expands when heated and contracts whencooled.
 3. The method of claim 1, wherein the additive manufacturingprocess is a 3D printing process.
 4. The method of claim 1, whereinmodifying the first pre-programmed tool path includes increasing thedistance of travel for the first pre-programmed tool path.
 5. The methodof claim 1, wherein modifying the first pre-programmed tool pathincludes decreasing the distance of travel for the first pre-programmedtool path.
 6. The method of claim 1, further comprising: moving thenozzle of the CNC machine the modified distance of travel along thefirst pre-programmed tool path.
 7. The method of claim 1, furthercomprising: modifying a distance of travel for a second pre-programmedtool path based on at least the Coefficient for Thermal Expansion (CTE).8. The method of claim 1, wherein rotational motion of the servomotor istranslated to linear motion according to a scaling factor.
 9. The methodof claim 8, wherein modifying the distance of travel for the firstpre-programmed tool path includes adjusting the scaling factor.
 10. Amethod for thermal compensation during an additive manufacturingprocess, the method comprising: receiving, at a CNC machine, informationrelating to a material used in the additive manufacturing process,wherein the received information includes at least a Coefficient forThermal Expansion (CTE) for the material; and adjusting a motion of theCNC machine based on at least the CTE of the material; wherein adjustingthe motion of the CNC machine includes adjusting a gearing mechanismassociated with a servomotor of the CNC machine.
 11. The method of claim10, wherein adjusting the motion of the CNC machine includes adjusting ascaling factor of the CNC machine.
 12. The method of claim 10, whereinthe servomotor controls movement of a print head of the CNC machine, andwherein adjusting the motion of the CNC machine includes adjustingmovement of the print head by adjusting a scaling factor of theservomotor.
 13. The method of claim 10, wherein the material is a fiberreinforced thermoplastic material.
 14. The method of claim 10, furtherincluding linearly translating a nozzle of the CNC machine via theservomotor and the gearing mechanism.
 15. The method of claim 10,wherein adjusting the motion of the CNC machine based on at least theCTE of the material includes adjusting a distance of travel for a firstpre-programmed tool path.
 16. The method of claim 15, further includingmodifying a distance of travel for a second pre-programmed tool pathbased on at least the CTE of the material.
 17. A method for thermalcompensation during an additive manufacturing process, the methodcomprising: receiving, at a CNC machine, information relating to amaterial used in the additive manufacturing process, wherein thereceived information includes at least a Coefficient for ThermalExpansion (CTE) for the material and a temperature of the environmentsurrounding the CNC machine; modifying a motion of a nozzle of the CNCmachine based on at least the CTE of the material and the temperature ofthe environment surrounding the CNC machine; wherein the CNC machineincludes at least one servomotor configured to linearly translate thenozzle to produce the motion; wherein rotational motion of theservomotor is configured to linearly translate the nozzle via a gearingmechanism; and wherein modifying the motion of the nozzle includesadjusting the gearing mechanism.
 18. The method of claim 17, whereinmodifying the motion of the CNC machine includes adjusting a scalingfactor of the nozzle.
 19. The method of claim 17, wherein modifying themotion of the nozzle includes modifying the motion of the nozzle alongmore than one axis.
 20. The method of claim 17, wherein the material isa thermoplastic material that expands when heated and contracts whencooled.